The third-generation iPad released Friday comes in the same 18 varieties as its predecessor, the iPad 2, but with more options when it comes to mobile broadband. Those options might seem obscure now, but you could wind up depending on them over the next months and years. Making the right choice now will save frustration later, and likely some cash.

The 18 varieties arise from three factors. First, you can get an iPad that works only over Wi-Fi, over Wi-Fi and AT&T’s 3G and LTE networks, and over Verizon Wireless’ 3G and LTE networks. AT&T and Verizon’s 3G and 4G networks are incompatible for roaming.

Each of those three models comes in 16GB, 32GB and 64GB capacities. That brings us to nine. You can pick a black or white bezel, which gets us to 18.

The fundamental choice comes down to wireless networking. The least expensive range of models ($499, $599, and $699, based on storage) has just Wi-Fi built in. If you know you’ll never want to use the iPad when a mobile network is available but not Wi-Fi, you can save $130 over otherwise identical 3G/4G models.

However, if you know you’ll want cellular-data access, or think it’s worth the investment for the future, you face a choice between AT&T and Verizon’s current 3G networks and under-construction 4G ones.

Verizon tends to come out on top in several regards, especially at launch. Apple says the new iPad can be used for “tethered” access, where the cellular modem in the device can relay data over USB, Bluetooth and Wi-Fi, turning the iPad into a router.

This feature, now called Personal Hotspot, has been in the iPhone for years, although AT&T delayed enabling it far longer than international carriers. For smartphones, AT&T and Verizon add a $20-per-month fee (but also toss in 2GB in extra usage) to enable an iPhone’s tethering option.

AT&T once again won’t commit to tethering, while Verizon says Personal Hotspot is not only available, but included in its three service-plan levels. Verizon also allows up to five devices to connect for tethering.

Verizon coverage

Verizon once had broader and more consistent coverage for its 3G network, as it invested earlier in what is now somewhat outdated technology, topping out at about 2 Mbps of real downstream speed.

AT&T has reportedly caught up, and it has a faster 3G network in place, which the iPad can take advantage of. AT&T’s HSPA+ network tops out at 21 Mbps of raw speed, or up to about 7 Mbps of real data sent downstream to a device. In practice, though, many tests show AT&T and Verizon’s 3G networks closer in performance.

That brings us to real 4G, the Long Term Evolution (LTE) standard that AT&T and Verizon are rolling out in the U.S. Verizon’s had it turned on in Seattle for some time, while AT&T has yet to commit to a date to turn it on here.

Seattle metro-area folks buying a Verizon model of the new iPad have immediate access to what Verizon says is about 5 to 12 Mbps of download speed. (Tests have found both it and AT&T’s network can jump to more than 20 Mbps downstream, likely because of the small number of LTE-compatible devices clogging the networks, which won’t be the case for long.)

Both AT&T and Verizon models of the iPad can be used to roam outside the U.S. The tablets have “unlocked” microSIMs, the cards used to handle billing and identity on 3G (but not LTE) networks used worldwide.

Even though Verizon’s 3G standard is incompatible with the dominant GSM standard that AT&T uses, Apple has built in full 3G GSM support. You can rent microSIMs abroad, and swap them in when traveling.

On price, Verizon has an advantage for heavier users. It offers monthly plans of 2GB for $30, 5GB for $50, and 10GB for $80. If you regularly plan to cross 6 or 7 GB a month, Verizon has the advantage. AT&T is sticking with previous offerings: 250MB for $14.99, 2GB for $25, and 5GB for $50. With prepaid offerings, in which service is charged in advance, if you exhaust your data allotment within a month, you can purchase a new plan and restart the monthly clock. Otherwise, you’re billed at the end of a month and can cancel renewal without a fee.

Postpaid service

Both carriers also offer postpaid service, which requires a credit check, and you’re billed monthly for service and overages. With those plans, Verizon charges $10 for each GB above your service plan used within the monthly plan period. AT&T charges $15 for additional units of 250MB on the 250MB plan, and $10 per GB for its 2GB and 5GB plans.

For Seattle and Eastside residents, the advantage right now is to Verizon, as well as to anyone who needs a mobile hot spot and would like to avoid the iPhone surcharge both AT&T and Verizon levy.

Over time, AT&T’s LTE coverage and, likely, pricing will come into line, making a future decision more about your own experience in getting good service, both the wireless signal and with customer support.